Dess and Martin showed the use of a hypervalent form of this element, in which it is bound to three acetoxy groups, in the oxidation of alcohols into aldehydes. Glycogen is stained brown by Lugol's solution, which contains the molecular form of this element with its potassium salt, and a similar combination is also used as a mordant for Gram's stains. A complex of poly-vinyl-pyrro-lidone and this element is commonly used as a disinfectant, and is called Betadine.  Seleni
Dess and Martin showed the use of a hypervalent form of this element, in which it is bound to three acetoxy groups, in the oxidation of alcohols into aldehydes. Glycogen is stained brown by Lugol's solution, which contains the molecular form of this element with its potassium salt, and a similar combination is also used as a mordant for Gram's stains. A complex of poly-vinyl-pyrro-lidone and this element is commonly used as a disinfectant, and is called Betadine.  Selenium dependent enzymes convert hormones containing this element from the T4 to the T3 form, and For 10 points, identify this element which is essential for the secretion of thyroxine, and whose deficiency leads to goitre. 
Dess and Martin showed the use of a hypervalent form of this element, in which it is bound to three acetoxy groups, in the oxidation of alcohols into aldehydes.
{iodine} [or I]